Thermal decomposition of nickel carbonyl

ABSTRACT

THE CARBON CONTENT OF NICKEL FORMED BY THE THERMAL DECOMPOSITION OF NICKEL CARBONYL IS REDUCED BY CARRYING OUT THE DECOMPOSITION IN THE PRESENCE OF NITROUS OXIDE (N2O), ADVANTAGEOUSLY AT 260*C. OR ABOVE. ADVANTAGEOUSLY A DECOMPOSER WITH NITRIDED STEEL WALLS IS USED. THE PRESENCE OF N2O DURING THE DECOMPOSITION OF NICKEL CARBONYL ALSO INHIBITS THE CONTAMINATION OF THE NICKEL PRODUCED WITH IRON.

United States Patent 3,694,186 THERMAL DECOMPOSITION OF NICKEL CARBONYLDavid Myers Llewelyn, Clydach, Swansea, Wales, assignor to TheInternational Nickel Company, Inc., New York,

Filed July 2, 1971, Ser. No. 159,471 Claims priority, application GreatBritain, July 7, 1970, 32,961/ 70 Int. Cl. B22f 9/00 US. Cl. 75-.5 AA 7Claims ABSTRACT OF THE DISCLOSURE The carbon content of nickel formed bythe thermal decomposition of nickel carbonyl is reduced by carrying outthe decomposition in the presence of nitrous oxide (N 0), advantageouslyat 260 C. or above. Advantageously a decomposer with nitrided steelwalls is used. The presence of N 0 during the decomposition of nickelcarbonyl also inhibits the contamination of the nickel produced withiron.

This invention relates to the production of metallic nickel, and moreparticularly to the production of metallic nickel by the thermaldecomposition of nickel carbonyl.

Nickel carbonyl has been decomposed to metallic nickel in various ways.For example, nickel carbonyl is passed over nickel pellets heated abovethe decomposition temperature of the carbonyl to deposit the nickel onthe surface of the pellets so that they increase in size. Decompositionof nickel carbonyl in the hot free space of a decomposer leads to theformation of nickel powder having variously shaped particles accordingto the conditions used. Another process is to decompose the carbonyl onthe surface of hot powder particles, which can be of nickel or of othermaterials that are to be coated with nickel, in the form of a fluidizedbed or a suspension of powder in a stream of carbonyl-containing gas.

Nickel produced by the thermal decomposition of nickel carbonyl containsa small amount of carbon, which increases with the temperature ofdecomposition. This carbon is probably formed by the decomposition ofcarbon monoxide according to the equation:

Some of the carbon is generally combined with with the deposited nickelas a nickel carbide, but in this specification references to the carboncontent of the nickel include free (graphitic) carbon.

It has now been discovered that the carbon and iron content of carbonylnickel can be reduced by carrying out the decomposition in the presenceof nitrous oxide (NO). The reduction of the carbon content becomes morepronounced as the temperature of decomposition is increased.

' It is an object of the present invention to provide a process forthermally decomposing nickel carbonyl to produce carbonyl nickel powderhaving low carbon contents.

Another object of the present invention is to provide a process forthermally decomposing nickel carbonyl to produce carbonyl nickel powderhaving low iron contents.

The invention also contemplates providing a process for producingcarbonyl nickel powder having low carbon and iron contents.

It is a further object of the invention to provide a process forincreasing the rate of thermal decomposition ice of nickel carbonylwithout increasing the carbon content of the product.

Other objects and advantages will become apparent from the followingdescription.

Generally speaking, the present invention contemplates the decompositionof nickel carbonyl. A decomposing zone is established and is heated to atemperature high enough to decompose nickel carbonyl but below thetemperature at which substantial carbon formation will occur duringdecomposition of nickel carbonyl. Nickel carbonyl and nitrous oxide arefed to the heated decomposing zone so that nickel carbonyl is decomposedin the presence of nitrous oxide to produce metallic nickel with a lowcarbon content.

The decomposing zone is normally established within a decomposer made ofmild steel, and it has previously been found that it is a greatadvantage to nitride the walls, e.g., by heating the vessel in thepresence of ammonia (advantageously, ammonia is admitted to thedecomposing zone and heated to about 500 C. for at least one hour). Ifthis is done the formation of black carbonaceous particles is largelyprevented. It has been found, however, that nitrous oxide does notnitride the decomposer walls, so advantageously the walls are nitridedin a previous operation.

The process can be carried on in the temperature range of 230 C. to 350C. Below 230 C. so small a proportion of the carbonyl is decomposed topowder that the process is not practicable on an industrial scale. Above350 C. a high proportion of filamentary aggregates are formed.Advantageously, the process is conducted at temperatures above about 260C. because the effects of nitrous oxide in minimizing carbon productionbecome more pronounced at temperatures above 260 C.

The amount of nitrous oxide can vary within wide limits. As little as 10parts per million of the carbonylcontaining gases, or even 1 p.p.m., iseffective, and the concentration may be as high as 1500 p.p.m. or evenmore without any of the advantages being lost. However, larger amountsthan 1500 p.p.m. or even 1000 p.p.m., besides increasing the cost, alsocreate problems in purifying the gases for further use, andadvantageously the amount of nitrous oxide added is kept as low aspossible, e.g., to 250 p.p.m. or even less.

The use of nitrous oxide will now be considered in more detail inrelation to the production of carbonyl nickel powder, that is to saypowder made by the thermal decomposition of nickel carbonyl vapour inthe hot free space of a decomposer.

Numerous tests were performed using a laboratory decomposer 10 inches indiameter having mild-steel walls that were externally heated in use. Inall the tests carbon monoxide gas containing from 7% to 9% of nickelcarbonyl was fed into the decomposer through an inlet at the top at arate (unless otherwise specified) of 2000 litres/hour. The nitrousoxide, when used, was injected into the gas stream at a measured rate atroom temperature. The temperature at the inlet to the decomposer wasmaintained at about 50 C. by water-cooling.

In the first set of tests the decomposer temperature (measured half-waybetween the axis and the wall) was maintained at 290 C. and theconcentration of the nitrous oxide was varied. Table I below shows theconcentration of the carbonyl by volume, the amount of nitrous oxideintroduced (in parts per million), the particle size of the powder asmeasured in the Fisher sub-sieve sizer, and the bulk density of thepowder and the carbon content of the powder. The first three tests, A, Band C are given by way of comparison. Tests A and B were carried out inthe decomposer before its walls were nitrided. Test C was carried outwith the walls of the decomposer in a nitrided condition, and so werethe other tests described in this specification. All the powdersproduced had a nitrogen content less than 0.001% and consisted ofdiscrete particles having a spiky appearance when exam- The effect ofvarying the temperature on the iron content of the nickel powderproduced is shown by the results set forth in Table IV.

ined microscopically under high magnification. 5 TABLE Iv TABLE I N Temptifiiiii 1? $3353? 1 N o ibe ehconce n- Fisher Bulk C.) (p.p.m.)(percent) tration tration size density Test No. (percent) (p.p.m.)(microns) (g./0c.) C(percent) l0 fig 9.0 4. 47 2.47 0.057 230 1, 0000.011 7. 0 a. 66 1. 99 0. 039 260 0. 010 8.0 4. 37 2.41 0.029 200 1250.004 7. 0 a. 53 2. 05 0. 020 260 1, 000 0. 004 8. 0 a. 91 2. 0. 020 2900. 014 7. 5 4. 47 2. 0. 020 290 125 0. 014 8.0 4.32 2.34 0.022 15 290 000.007 8.5 4. 47 2. 0. 020 320 0. 015 9. 0 4. 5 2. 4s 0. 020 320 125 0.01a 8. 5 5. a 2. 5e 0. 010 320 1, 000 0. 014

This table shows that at all the nitrous oxide concentrations used therewas a marked reduction in the carbon 20 The results in Tables III and IVshow that at 260 C. content of the powder. the iron content is reducedto a remarkably low level. It

The eifect of varying the temperature of decomposrappears that theconcentration of nitrous oxide required tion is shown by the results inTable II. All the tests were to bring about a significant improvementincreases as the carried out with the walls of the decomposer in thenidecomposition temperature increases. trided condition. 25 Although thepresent invention has been described in TABLE II Carbonyl N20eoncenconcen- Fisher Bulk tration tration size density 0 (percent)(p.p.m.) (microns) (g./cc.) (percent) It will be seen that while thecarbon content of the conjunction with preferred embodiments, it is tobe underpowders increases as the decomposition temperature 18 stood thatmodifications and variations may be resorted increased, in each case thepresence of nitrous oxide durto w thout departing from the spirit andscope of the ining the decomposition lowered the carbon content. Theventron, as those skilled in the art will readily understand. shape andnitrogen content of the powder particles I 1Ch modifications andvariations are considered to be formed at 250 c. and 320 c. were similarto that of wlthln pu and scope of the invention and pthose formed at 2900., though the particle size was pended'clalmsgreater at 260 C. andsmaller at 320 C. I (3181111! A further advantage of using nitrous oxideis that its A pr thermally decomposing nickel presence during thedecomposition of nickel carbonyl bonYl Whlch P a l Shmg a decomposingzone, appears to inhibit the contamination of the nickel proheatlng thedecomposlpg Zone t0 a temperature high duced with iron. This effect isshown by the results in enough to (16009113056 mckel Y the t m-Table'III, which set forth the iron contents of nickel pow- Pemtul'e fWhlch carbon formation vvlll Occur during ders formed by thedecomposition at 290 C. of nickel 9 P of nickel f y i feedlllg themcarbonyl containing traces of iron carbonyl, using the P 5 11100118OXIdo in Small but efl'ective amounts same decomposer with nitridedsteel walls as in the previto n llmml ze the decomposltlon of Carbon mnoxide and ous tests, with and without the presence of nitrous oxidefeedmg nickel o y t0 the heated decomposing Z0116 in the concentrationsshown. In each case the concentrato decompose the nickel CaIbOHYI t0metallic el With tion of nickel carbonyl was in the range 7-9% byvolume, a low carbon content the balance of the gas being carbon mon id0 2. The process as descr1bed in claim 1 wherein the decomposingrone 1sthe free space of a reactor and the free space is maintained at atemperature between about 230 C. and 350 C. to produce carbonyl nickelpowder. 3. The process as described in claim 2 wherein the free TAB IIIspace of the reactor is bounded by nitrided mild steel N10 walls.

ggg gg g 4. The process as described in claim 1 wherein the con- Test No(p.p.rn.) (percent) centration of nitrous oxide in thecarbonyl-containing gas M14 is between about 1 part per million and1,500 parts per 0.015 million. 8:85: 5. The process as described inclaim 4 wherein the 0. 015 carbonyl-containing gas contains betweenabout 10 parts 8:83}, per nullion and 1,000 parts per million nitrousoxide 0.005 to produce carbonyl nickel powder with low carbon con- 6 6.The process as described in claim 4 wherein the References Cited 1:10:32fghcglyat :dgegorgposed at a temperature between UNITED STATES PATENTS7. The process as described in claim 6 wherein the 2,844,456 4/1958Llewelyn 75 0-5 AA nickel carbonyl is decomposed at a temperature of at6 least about WAYLAND W. STALLARD, Prlmary Exammer

